PRIOR ART
The invention applies to electromagnetic field shaping devices.
More particularly the device applies to medically related electromagnetic field shaping devices for shaping internal fields and periphery or perimeter fields.
Numerous methods for shaping external beam radiation therapy fields have been developed. These include custom milling or casting of lead blocks and the use of lead shot either poured into styrofoam forms or incorporated into wax. Fordham, E. W.; Gibbs, G. G.; Henderickson, F. R., Shield Construction of extended field therapy of Hodgkins's Disease, Radiology 92: 1374-1376 (1969). Page, V.; Gardner, A.; Karzmark, C. J.; Physical and Dosemtric aspects of the radiotherapy of malignant lymphomas, Radiology 96: 609-618, (1970); Edland, R. W., Hansen, H.; Irregular field Shaping for Co-60 teletherapy Radiology 92: 634-635 (1969); Custom field shaping using cast Lipowitz's metal, however, has probably become the most common method of producing irregular shaped fields for external beam radiation therapy treatment. Radiology 108: 407-411, (1973); Powers, W. E., Kinzle, J. J., Demidecki, A. J., Bradfields, J. S., Feldman, A. A new system of field shaping for external-beam radiation therapy Radiology 48: 924-926, (1975); Marshall, T. J., Mott, G. T., Grieveson, J. H. A technique for using low melting point alloy for individual patient shielding in radiology Applied Radiology 6: 115, (1977); Luk, K. H., Castro, J. R., Meyler, T. S., Potter, L., Purser, P. R. Individual low-melting alloy shielding blocks for external-beam radiation therapy American Institute of Physics, 456-476, (1983); Purdy, J. A. Secodanring Field Shaping In: Wright, A. E. and Boyer, A. L. eds, Advancing in Radiation Therapy Treatment Planning, New York, N.Y. Specialized applications for field shaping or tissue shielding have included construction of individualized midline blocks for external beam treatment of pelvic malignancies and gonadal shields in the treatment of lymphoid malignancies. Radiology 107: 611-614, (1973); Walz, B. J., Perez, C. A., Feldman, A., Demidecki, A. J., Powers, W. E., Individualized compensating filters and dose optimization in pelvic irradiation Radiology 117: 226(1975) Purdy, J. A., Stiteler, R. D., Glasgow, G. P., Mill, W. B., Gonadal Shield. Other specialized blocking applications have included construction of individualized irregular field blocks for electron beam and superficial X-ray treatment. Int. J. Radia. Onc. Biol. and Phys. 2: 791-795, (1977); Goede, M. R., Gooden, D. S., Ellis, R. G., Brickner, T. J., Jr., A versatile electron collimation system to be used with electron cones supplied with Varian's Clinac 18. Radiology 132: 490, (1979); Purdy, J. A., Abrath, F. G., Perez, C. A., Field shaping for electron-beam radiation therapy. Br. J. Radiol. 54: 805-807 (1981); Baily, B., Coe, M. A., Hearnden, T. M., A new technique for radiation shielding in superficial x-ray therapy.
Irregular field shaping in external beam radiation therapy treatment has allowed treatment of areas of interest and sparing of uninvolved normal tissues. Casting of Lipowitz's metal and similar alloys to produce customized irregular fields is well accepted in many departments. Hand blocks, however, continue to be used for shielding in some cases. The method of adjustable field blocking described in this report is clinically useful and can fill the gap between a full custom block and simple hand blocks in appropriate cases. Advantages of this system include rapid field set up easy field adjustment and improved day to day reproducibility of field set up compared to simple hand blocks. The blocking system is cost effective and has been shown to produce high quality treatment in clinical use.
Custom shaped shielding blocks of Lipowitz's metal and similar allows improve the uniformity of daily treatment fields and are easy to use once they are constructed. Constructing shielding blocks from Lipowitz's metal, however, requires significant time and materials. Some clinical treatment situations frequently do not require a full customized field block. Palliative cases where fields are commonly shaped by simple hand blocks are an example. Other examples include some whole pelvic fields, some simple head and neck fields and some supraciavicular/auxiliary fields where shoulder blocking is required. Daily field shaping using simple hand blocks connected to standard blocking trays, such as in the case of lateral and angled fields, may allow only limited positioning further complicating field setup.
Support plates with slots having shielding members disposed in the slot by way of an adjustable and removable securing means and removable securing means where the slots are transversally mounted other slots. These shielding means are often made in the shape of the organ to be protected. U.S. Pat. Nos. 4,472,637 and 4,266,139 by Sportell, et al exhibit this technique. The most important drawback which these techniques and patents attempt to address is maximizing the flexibility of the system to provide different field shapes for internal blocking as opposed to perimeter fields.
The present patent not only allows for internal blocking but also allows for perimeter field blocking.
The prior art encompasses the use of slotted trays and blocks for mounting thereon. Shielding block molds are fashioned at the appropriate target to tray distance for the external beam treatment unit from high density polyethylene foam using a hot wire cutting device. Lipowitz's metal or similar alloys have been used to cast the shielding blocks and, milled or cast lead blocks may also be used.
It is desirable to minimize the amount of block cutting used in making fields. In response to the need for a simple flexible method of field shaping, a new adjustable blocking system was developed which allows a greater range of field adjustment with fewer blocks.
The system allows a wide latitude of placement of the shielding blocks on the blocking tray. The blocking system has been shown to be cost effective and allows rapid setup of treatment fields. It also allows daily blocking adjustment if required and has been shown to produce high quality reproducible fields in clinical use. This system also affords the advantage of allowing easy field adjustment on a daily basis, e.g. lens blocks on bilateral whole brain fields. This system is also cost effective since the mounted blocks can be used repeatedly thereby reducing the time and material required to fabricate customized cast blocks.
The primary improvement over the prior art with the instant invention is that it allows for a great degree of perimeter field adjustment not available in the prior art.
Another improvement is that the invention allows for easy adjustment of both perimeter and interior blocking.
Another improvement is that the invention allows for an inexpensive and reproduceable product and method for using the product for shaping electromagnetic fields.
These and other improvements will become obvious from the drawings and specifications and drawings attached hereto on which like numerals represent like portions of the invention.